Processes for the preparation of olefins are known in the art.
U.S. Pat. No. 6,797,851 describes a process for making ethylene and propylene from an oxygenate feed using two or more zeolite catalysts.
In a first stage, an oxygenate feed is contacted with a first zeolite catalyst containing ZSM-5. The resulting conversion product contains an olefins composition. The olefin composition from the conversion reaction, with or without prior separation of ethylene and propylene, is then contacted with another zeolite catalyst in a second stage. The catalyst of such second stage is a one-dimensional zeolite having 10-membered ring channels, including ZSM-22, ZSM-23, ZSM-35, ZSM-42 or mixtures thereof. The eventual product comprises ethylene, propylene and C4+ olefins. The C4+ olefins may be partly recycled to the first stage as olefinic co-feed of the oxygenate feed. In the only example, pure methanol is converted by a two-step process into several olefins. In the process, typically use is made of a single reactor with a stacked bed configuration wherein the first stage is carried out in a first zeolite catalyst bed and the second stage is carried out a second zeolite bed (see FIG. 1 of U.S. Pat. No. 6,797,851). Alternatively, the two stages are carried out in two separate reactors (see FIGS. 2-5 of U.S. Pat. No. 6,797,851). The catalyst used in this process can be regenerated to remove carbonaceous deposits (coke) from the catalysts used. In case a single reactor is used this can be done periodically by ceasing the flow of feed to the reactor, introducing a regeneration medium, ceasing flow of the regeneration medium, and then reintroducing the feed to regenerated catalyst. In case two separate reactor are used regeneration will occur periodically or continuously outside the reactor by removing a portion of the deactivated catalyst to a separate regenerator. When the catalysts in both the two separate reactors need to be regenerated two separate regenerators are used.
During the regeneration, coke is removed from the catalyst. The extent to which coke is removed from the catalyst is an important feature of the process. If insufficient coke is removed, the selectivity of the oxygenate conversion is affected. However, exposing the catalyst to conditions that remove more coke may lead to an undesired reduction of the catalyst activity.
It would be desirable to have an improved process, in which olefins, such as ethylene and/or propylene, can be prepared in a single reaction stage which can be operated highly efficiently and in a cost-effective manner, with an improved control of the extent of coke removal from the catalyst.